from The American Heritage® Dictionary of the English Language, 4th Edition

transitive v. To form a correct estimate or conjecture of: guessed the answer.

transitive v. To suppose; think: I guess he was wrong.

intransitive v. To make an estimate or conjecture: We could only guess at her motives.

intransitive v. To estimate or conjecture correctly.

n. An act or instance of guessing.

n. A conjecture arrived at by guessing.

from Wiktionary, Creative Commons Attribution/Share-Alike License

n. A prediction about the outcome of something, typically made without factual evidence or support.

v. To reach a partly (or totally) unqualified conclusion.

v. To solve by a correct conjecture; to conjecture rightly.

v. to suppose (introducing a proposition of uncertain plausibility).

from the GNU version of the Collaborative International Dictionary of English

n. An opinion as to anything, formed without sufficient or decisive evidence or grounds; an attempt to hit upon the truth by a random judgment; a conjecture; a surmise.

intransitive v. To make a guess or random judgment; to conjecture; -- with at, about, etc.

transitive v. To form an opinion concerning, without knowledge or means of knowledge; to judge of at random; to conjecture.

transitive v. To judge or form an opinion of, from reasons that seem preponderating, but are not decisive.

transitive v. To solve by a correct conjecture; to conjecture rightly.

transitive v. To hit upon or reproduce by memory.

transitive v. To think; to suppose; to believe; to imagine; -- followed by an objective clause.

from The Century Dictionary and Cyclopedia

To form, without certain knowledge, but from probable indications, a notion concerning; form a provisional or an imperfect opinion concerning; conjecture; surmise.

To conjecture rightly; solve by a correct conjecture; form a true opinion of: as, to guess one's design; to guess a riddle.

In a loose use, to believe; think; suppose; imagine: with a clause for object.

[This use is common in English literature from the first appearance of the word; but it is now regarded as colloquial, and, from its frequency in the United States, it is generally supposed by Englishmen to be an “Americanism.” By an easy extension guess is used for think, believe, or suppose, even where the meaning is not at all conjectural, but positive, and it is then logically superfluous, serving merely to make the assertion less abrupt: as, I guess I will go now (that is, I am going now); I guess I know what I'm about (that is, I know what I am doing). In most instances this use probably arises from a desire to avoid positive assertion, or from some feeling of hesitation or uncertainty.] Synonyms Imagine, Presume, etc. See conjecture.

To form a conjecture; judge or conclude from incomplete or uncertain evidence: commonly with at or by.

n. A notion gathered from mere probability or imperfect information; a judgment or conclusion without sufficient or determinate evidence; a conjecture; a surmise: as, to act by guess.

This time, it's the credibility of the "Bush-bashers," a diaphanous term which we can only guess translates as "anyone who disagrees with the president's administration" (the majority of America, to beat a dead horse), which is the problem.

When asked to weigh in on how Democrats are handling the issue by Fox News host Sean Hannity, Paul said, "Well, my guess is they think they will lose on the issue and they see that the American public doesn't buy this 'soak the rich' or 'tax the rich.'"